“Key to understanding the future is understanding basic laws of nature and their application in inventions, machines, and therapies which will redefine our civilization deeply in the future.” – Michio Kaku: Physics of the Future, 2012
In the engineering world, unforeseen situations often occur. Solving one problem can usually create new obstacles and open a number of new questions. Answers to them, however are sometimes closer to us than we think.At a time when Japanese bullet-trains, to all known Shinkansens, amazed the world with their record-breaking achievements, engineers of Japan Railways West faced unusual challenges. Although 500 series trains were able to travel 300 km/h even in the early 1990s, levels of noise that they created at such a speed exceeded far over the permitted noise standards. In 1975 Japan Environment Agency issued one of the world’s strictest noise standards for the railroad transport. Shinkansen trains were not allowed to exceed noise limit of 75 dB.
In those days, engineers wanted to try with even faster speeds (350 km/h), but two main problems prevented them from doing so. One problem were noise and turbulence produced by pantographs at high speeds. Another, bigger problem was the appearance of a sonic boom, better known as a “tunnel boom“. Sonic booms would appear when trains would pass through tunnels at high speeds. Reason: big difference in pressures.
Residents of the areas near the tunnels were unexpectedly surprised by this phenomenon so they expectedly reacted. Since Japan is a mountainous country with many tunnels, problem was even bigger. The largest western cities, Shin-Osaka and Hakata are even today connected by a line whose one half consists of tunnels.
Engineers have been given the task of reducing travel time from Shin-Osaka to Hakata, and the issue that was imposed was the following: How to increase Shinkansen speed and simultaneously reduce the unpleasant noise to a satisfactory level? Elimination of the sonic boom appearance became a priority!
First Da Vinci Principle: CURIOSITÀ – insatiable curiosity
Engineer Eiji Nakatsu, chief engineer at the Technical Development Department in Japan during those times, has demonstrated the true power of engineering. Not only did he offer the solution, but he has also changed the way engineers solved challenging tasks of their time. Eiji didn`t have the technology we have today, so he was forced to follow his intuition. He realized that the “tunnel boom” actually happened because of the unfavourable aerodynamic profile of Shinkansen, which made it difficult for him to pass through tunnels. Since the problem was of aerodynamic nature, ingenious Nakatsu decided to find answers in nature. Idea: Birds!
“Surely there are birds that naturally encounter similar problems …” he thought. After seeing an article in the newspaper, Nakatsu headed for the Wild Bird Society in Osaka where he visited his colleague Seichi Yajimi, an aviation scientist. He was surprised how much aviation technology was already based on studying the functions and body structures of birds.
Engineer Yajimi has observed birds for many years. In their physiology and anatomy, he found answers how to overcome the most difficult aerodynamic barriers in the aviation industry. After some time spent in Yajimi’s fellowship, Nakatsu’s curiosity was rewarded. Three animals inspired him to solve the noise problem.
How did an owl and a penguin solve the pantograph problem…
At speeds greater than 200 km/h, the unsightly shape of the Shinkansen 500 Series pantograph produced excessive turbulences and impermissible noises. Turbulence was caused by so-called Kármán vortex street phenomenon. Huge vortexes would emerge because of the way that air passed around the pantograph at high speeds. Main issue was, therefore, the shape of the pantograph. How this vortex phenomenon occurs, you can read by clicking this link.
Nakatsu asked himself a question: How do birds cope with turbulences during flight?
Seeking an answer, he discovered that owls, true masters of night hunt, emit far less sound than other birds when flying. If they want to be successful in hunt at night, they need to be silent – and they are. Prime feathers of the owl`s wings have micro-serrations (plise) that segregate vortexes and break large vortices – the noise producers to much smaller ones. Smaller vortices cause significantly less aerodynamic vibrations. That is one of the reasons why owls can seamlessly approach to their prey.
According to Nakatsu’s ideas inspired by owls, engineers made structural adaptations on the top elements of the pantograph. After many tests in air tunnels, effort was paid. Micro-serrations, made on the upper element of pantograph, produced less turbulence thanks to breaking bigger vortexes into smaller which ultimately reduced noise. Interesting fact is that, during those tunnel testings, real preserved owls from Osaka Zoo were used. Engineers needed four years to successfully finish this project.
Another animal that has influenced change of the pantograph`s shape is the Adélie penguin. Specific body shape of this penguin is like a spindle which allows it to effortlessly move in the water. Guided by this idea, engineers changed the shape of the pantograph based on the shape of a body of Adélie penguin. After several test phases, it has been proven that the new design of pantographs reduces wind resistance.
By installing new pantographs in year 1994, Shinkansen could travel at the speed of 320 km/h with noise below 75 dB. One question still remained: How to solve the problem of “tunnel boom”?
Learning from nature
The problem of sonic boom was far more complex than the pantograph problem. When a train is passing through a tunnel at a high velocity, sudden pressure changes occur. Low frequency waves are then generated which results in sound burst and aerodynamic vibrations. Sound that appears is similar to a shotgun. Any increase in train speed in tunnels increases the pressure three times, so it is not a surprise that residents (in the area of 400 m from the tunnel) complained for unbearable sounds.
Nakatsu wondered where would in nature exist an organism that overcomes a similar problem – the problem of fast moving from a light to a dense medium! Birds that hunt fish by suddenly entering water came into his mind. “Does the intensity of the immersion into water affects the success in hunting a fish?” – he asked.
Nakatsu has found a solution that left nobody indifferent – a Kingfisher bird. He was fascinated by the ability of this marsh bird to get into the water with extraordinary ease – no turbulence, no drops of rain! Thanks to the specific shape of their beak and head, Kingfishers literally slide through the water. It is the most efficient animal in the world in terms of transition from low pressure media (air) to high pressure medium (water).
Kingfisher passes from one fluid (air) to the other 800 times denser (water), without the appearance of sound barriers.
Of all the forms of metal bodies used in the experiments in the air tunnels, the shape designed by the parabolic shape of the Kingfisher`s beak turned out to be the best solution. This is how the present aerodynamic design of the Sanyo Shinkansen 500 Series front was created. A new, 15 m long train conus reduced the sound to appropriate level. These trains could finally drive through tunnels at a speed of 300 km/h without the appearance of “tunnel booms”. Passengers could now travel from Shin-Osaka to Hakata in 2 hours and 17 minutes, unlike the previous 2 hours and 32 minutes, without unpleasant noises.
Nakatsu used concepts of nature and applied them to the railway technology. Today, this process of using nature as a teacher for technological advancement is called biomimicry.
Why do we need traffic engineers?
In year 1997, JR West launched redesigned version of the Shinkansen 500 Series. This version was 10% faster, quieter, and 15% more energy-efficient. Air resistance was reduced by 30% compared to the previous version.
Since its inauguration in 1964, Shinkansen has been known for its reliability, safety and schedule accuracy. Until today, there are no casualties in terms of collisions or derailments despite numerous earthquakes and typhoons. The average delay is about 10 seconds. Using Shinkansen as a mean of transport in Japan is saving annually about 1,800 lives, according to estimations. Ecological impact reduced healthcare costs and saved future generations from living in major CO2 emissions.
By solving noise challenges, Japanese engineers have shown that they care about the mobility of their citizens and safety of future generations. Although they have different professions, traffic and transport science is what unites them. Impact of transport science and technology should always be viewed through long-term social benefits. That is why we are studying and innovating in the first place, that is why we need traffic engineers.